OBSERVATORY

By HENRY FOUNTAIN

Published: August 3, 2004

Tracing a Meteorite's Origins

In the world or art and antiques, provenance counts for a lot. Knowing the history of an object -- who owned it and when -- can greatly add to its value.

For scientists who study meteorites for a living, provenance counts for a lot, too. The problem is that other than knowing that a particular rock was once a piece of an asteroid or, in rarer cases, a chunk of the Moon or Mars, there is little else that scientists can know about its origins.

Now, an international team led by Swiss scientists has pieced together the most detailed history yet of a meteorite, a half-pound piece of the moon that was discovered in Oman in 2002. They know when and where it was formed, when it was knocked into space (to eventually land on Earth) and what happened to it in the intervening years.

For one thing, the scientists say in a paper in the journal Science, the meteorite's chemical composition -- it is enriched with potassium, phosphorous and rare earth elements -- means that it could have come only from the Imbrium basin, a large area on the Moon's near side.

The basin was formed by the impact of a large asteroid 3.9 billion years ago; using isotopic dating techniques, the scientists showed that the meteorite, a rock called an impact melt breccia, was formed at the same time.

The scientists were also able to determine other seminal events in the meteorite's existence. Twice -- 2.8 billion and 200 million years ago -- it was stirred up by other impacts. That helped pinpoint the rock's location even further, to an impact area in the basin called the Lalande Crater.

But something had to get the rock to Earth. That something was a final impact, 340,000 years ago, that hurled the rock high and fast enough that it escaped the Moon's gravity, eventually to be captured by Earth's. It landed in Oman about 10,000 years ago.

The Dingoes' Long Lineage

Australian dingoes didn't fall from the sky, but there's a certain amount of mystery about their origins as well. The dogs had the run of the continent long before Europeans arrived, but just how and when they came to be there has been unclear.

A detailed DNA analysis of dingoes and other dogs and wolves from around the world has gone a long way to pinning down the animal's history. The research, by scientists from Sweden, the United States, Australia and New Zealand, was published in The Proceedings of the National Academy of Sciences.

The analysis of samples from 211 dingoes showed that mitochondrial DNA sequences from all of them were identical or very similar to a single type. This means that the dingo must have its origins in the arrival in Australia of a small group of dogs (perhaps even a single pregnant female) or of a larger group that had become genetically uniform. The researchers calculated that this ''founding event'' happened about 5,000 years ago.

As to where those ancestral dogs arrived from, the researchers noted that the same mitochondrial DNA type was also found among dogs from East Asia. This suggests that the dogs were brought to Australia by seafarers during the expansion of the Austronesian culture from Taiwan to the Philippines and Indonesia, which according to current theories probably began about 6,000 years ago.

Mars for the Masses

A NASA Web site intended for Mars scientists has proved so popular that it is, in effect, being turned over to the public.

The site, Marsoweb, was developed so that scientists could help pick landing sites for the current rover expeditions. But the various maps and other data lured many nonscientists to the site, so the site has been modified to make it easier for the public to get a feel for the Martian terrain. Not every feature is operational yet, but you can try it out at marsoweb.nas.nasa.gov.

When Squirrels Screech

It may be, as the tag line for the movie ''Alien'' put it, that in space no one can hear you scream. But for some squirrels, that's true right here on Earth.

Zoologists at the University of Manitoba have discovered that a species of prairie-dwelling squirrel makes high-frequency calls that are far beyond the reach of human hearing. The squirrels use these silent screams to warn others of impending danger, the scientists say in the journal Nature. While bats use ultrasound to navigate and find prey, the squirrels' screeches appear to be the first known example of ultrasonic alarm calls in an animal.

Dr. James F. Hare, an associate professor and the author of the paper with a graduate student, David R. Wilson, has studied Richardson's ground squirrels for years in his work on social behavior and communication in animals.

Dr. Hare first noticed something odd about them more than a decade ago when he observed a squirrel that looked as if it was vocalizing, but no sound came out.

''To be honest, I thought the squirrel had lost her voice,'' Dr. Hare said. ''But it became apparent over the next few days that other squirrels were doing this. And they were switching back and forth between audible and inaudible calls.''

He discovered that the squirrels were making very short screeches at a frequency of about 50 kilohertz. Because all he could hear, close up, were the faint sounds of air rushing out of a squirrel's mouth, he called these vocalizations ''whisper'' calls.

Experiments showed that the calls, like audible screeches, made nearby squirrels assume alert postures and be on the lookout for predators.

But this ''postural vigilance'' was not as pronounced with the ultrasonic calls; the squirrels would lift their heads but not stand on their rear feet, for example.

So, Dr. Hare said, the ultrasonic calls may be a kind of covert signal used only when predators are very near.

Birds are not sensitive to ultrasound, he said, ''So it's possible that you use an ultrasonic call when you don't want a predator to pick you off.''

Richardson's squirrels live with kin in close-knit colonies, so the ultrasonic calls, which are directional and of short range, may be a selective signal as well.

''It may be a way to give an alarm that only goes out to your relatives,'' Dr. Hare said.